What is the difference between positive and negative Token tuning in RockShox DebonAir+ rear shocks?

Positive Bottomless Tokens reduce volume in the positive air chamber of the air spring, which causes the air spring curve to ramp up at the end of the travel to make it harder to bottom out. Negative Tokens reduce volume in the negative air chamber of the air spring, which causes the air spring to feel firmer at the beginning of the travel and more linear at the end of the travel to make it easier to achieve bottom out. See the RockShox Setup and Tuning Guide for best practices for setting air pressure, High Speed Compression, Low Speed Compression, and tuning with air can Tokens.